The term “junk food” is used to describe food which is low in nutritional value, with a comparatively high caloric value. Many people try to avoid or limit junk food in their diets, out of concerns that such food is not healthy, despite the fact that numerous food manufacturers produce a range of products which could be considered junk food. Nutritionists, doctors, and other health advocates often work to educate people about junk food, encouraging them to eat well balanced diets which contain a high proportion of healthy foods.

This term was coined in 1972 by advocates at the Center for Science in the Public Interest who wanted to raise public attention about the issue of foods with a high caloric value and a low nutritional value. For manufacturers, producing such foods has great appeal, as they tend to be cheap to make and easy to handle. They also have an extended shelf life, making them easy for stores to stock and sell.

Foods which fall under the umbrella of “junk food” vary, depending on a number of factors. Snack foods like chips, candies, and so forth are generally universally agreed upon as junk food, and some people also lump fast food like hamburgers, pizza, and fries into the junk food category. In some communities, ethnic takeaway food like gyros, Indian curries, tacos, fish and chips, and so on is also considered to be junk food.

Often, the foods which someone considers to be junk food are very telling. Definitions of “junk food” tend to hinge on someone's class and social status. People with more money tend to have a broader definition of junk food, causing some people to accuse them of class snobbery, while lower-income individuals may recognize less foods as junk food. Especially in the case of ethnic foods, a classification as “junk food” could be perceived as rather offensive, given that such foods have been prepared and consumed for centuries, and many are actually quite healthy.

As a general rule, no matter what one classifies as junk food, such foods are perfectly safe to eat, as long as they are integrated into a well balanced diet. There's nothing wrong with having some potato chips now and then, but consuming a diet based primarily on junk food is a cause for concern. Because junk food often lacks useful vitamins and minerals, people who eat an exclusive diet of junk food may suffer from nutritional deficiencies which could cause health problems, and they may experience other physical issues like indigestion as a consequence of eating a large amount of junk food.

In some regions of the world, advertising of junk food is carefully controlled and monitored, out of the concern that such foods often appeal to children. Advertisers may be specifically prohibited from making advertising which targets children, for example, and any claims made about the nutritional benefit of foods are typically closely evaluated to determine how factual they are.